This is best seen when multiple heroes use their phasers side by side, and the angles differ. Say, in "Arsenal of Freedom" where Data, Riker and Yar aim at the same target:
(And this angle is particularly weird)
Or in "Too Short a Season" where Yar and Worf hold their weapons identically yet cut different parts of the wall:
It seems that the hand phaser typically is more like a whip than a gun in nature: one flings the beam to the target, and it sticks there, regardless of the orientation in which the weapon handle is thereafter held. Except that the hand phaser can do the flinging even before initiating the beam.